Phosphazene high polymers with N=PR(3) (phosphazo) side groups are of interest from both the theoretical and potential technological points of view. High polymeric monophosphazophosphazenes were prepared with trifluoroethoxy, phenoxy, anilino, and propylamino side groups. Small-molecule cyclic counterparts were also synthesized as model systems for the macromolecular reactions. These compounds were prepared using both (trichlorophosphazo)pentachlorocyclotriphosphazene (N3P3Cl5NPCl3) and (trichlorophosphazo)pentafluorocyclotriphosphazene (N3P3F5NPCl3) as the starting materials. Specifically, the synthesis of monophosphazophosphazene polymers through the thermal ring-opening polymerization of N3P3Cl5NPCl3 at 150-180 degrees C or of N3P3F5NPCl3 at 200-210 degrees C is reported. Differences in the reactivity of the phosphazochloro- and the phosphazofluorophosphazenes to halogen replacement reactions were found at both the cyclic trimeric and high polymeric levels. In general, replacement of the chlorine atoms by organic groups was achieved with greater ease than the replacement of fluorine atoms. For the reagents studied, the replacement of halogen atoms by sodium trifluoroethoxide was more facile than with the other nucleophiles. A comparison is made between the properties of monophosphazophosphazenes, classical phosphazenes, and 1,1-diphosphazophosphazenes.